Method and apparatus for determining signal quality

ABSTRACT

A method comprises determining maximum and next-maximum correlation candidates for a symbol of a modulated signal, calculating a scalar relationship between the maximum and next-maximum correlation candidates, deriving signal quality associated with the modulated signal based on the scalar relationship, and altering a characteristic based on the derived signal quality.

RELATED APPLICATION

This application is a Continuation of U.S. Ser. No. 10/105,130, filedMar. 21, 2002, which application claims priority benefit under 35 U.S.C.§119(e)(1) to U.S. Provisional Application No. 60/334,347, filed Nov.29, 2001, entitled Method and Apparatus For Determining Signal Quality,all of which are incorporated herein fully by reference in theirentirety.

TECHNICAL FIELD

This invention is generally concerned with modulated signal receiverperformance, and is particularly concerned with techniques for assessingperceived signal quality of a modulated signal derived from processingone or more coded symbols contained within the signal.

BACKGROUND OF THE INVENTION

The past few years has witnessed the ever-increasing availability ofrelatively cheap, low power wireless data communication services,networks and devices, promising near wire speed transmission andreliability. One technology in particular, described in the IEEEStandard 802.11b-1999 Supplement to the ANSI/IEEE Standard 802.11, 1999edition, collectively incorporated herein fully by reference, and morecommonly referred to as “802.11b” or “WiFi”, has become the darling ofthe information technology industry and computer enthusiasts alike as awired LAN/WAN alternative because of its potential 11 Mbps effectivedata transmission rate, ease of installation and use, and transceivercomponent costs make it a real and convenient alternative to wired 10BaseT Ethernet and other cabled data networking alternatives. With802.11b, workgroup-sized networks can now be deployed in a building inminutes, a campus in days instead of weeks since the demanding task ofpulling cable and wiring existing structures is eliminated. Moreover,802.11b compliant wireless networking equipment is backwards compatiblewith the earlier 802.11 1M/2 Mbps standard, thereby further reducingdeployment costs in legacy wireless systems.

802.11b achieves relatively high payload data transmission rates throughthe use of orthogonal class modulation in general, and, moreparticularly, 8-chip complementary code keying (“CCK”) at a 11 MHzchipping rate. As such, bitstream data is mapped into nearly orthogonalsequences (or code symbols) to be transmitted, where each chip of thecode symbol is quaternary phase modulated. An 802.11b compliant receivercorrelates the received CCK modulated signal with 64 candidate waveformsto find the most likely code symbol, from which the bitstream data isrecovered through reverse mapping. The high-rate physical layer PLCPpreamble and header portions are still modulated using the 802.11compliant Barker spreading sequence at an 11 MHz chipping rate,resulting in a 1 or 2 Mbps effective header and preamble transmissionrate depending on whether DBPSK or DQPSK modulation is employed.

CCK was chosen in part because of its strong inherent resistance tomultipath interference, which is likely to be encountered in the typicalin-building deployment. Nevertheless, the confluence of strictpower/noise limits specified for operation in the 2.4 GHz ISM band andmegabit+ expected data throughput rates limits conventional 802.11b tojust a 100 or so feet between stations, depending on the number ofinterposing radio obstructions and reflections.

Thus 802.11b remains susceptible to multipath interference, and toreception errors produced by inter-symbol (“ISI”) and inter-chipinterference (“ICI”) in particular. To combat this, designers havesought to improve receiver performance, at least with respect to CCKcode symbol demodulation by using active equalization techniques.However, such techniques do not appear to take into account symbolprocessing reliability or errors, much less track such errors, nor alterthe transmission environment when post symbol processing signal qualitydegrades.

SUMMARY OF THE INVENTION

To address these and other perceived shortcomings, the present inventionis directed to a method, program product, and apparatus that determinesa signal quality associated with a symbol modulated signal based on ascalar relationship based on at least one of a comparison of pluralcorrelation candidates for a symbol in the modulated signal or acomparison of the vector corresponding to a decided symbol against areference. In accordance with one aspect of the present invention, amethod and apparatus are disclosed which involve determining maximum andnext-maximum correlation candidates for a symbol perceived in themodulated signal, calculating the scalar relationship between themaximum and next-maximum correlation candidates, and deriving a signalquality associated with the modulated signal based on the scalarrelationship.

In accordance with another aspect of the present invention, a method andapparatus are disclosed which involve determining a decided symbol forthe symbol perceived in the modulated signal, calculating a scalarrelationship between a vector corresponding to the decided symbol and areference, and deriving a signal quality associated with the modulatedsignal based on the scalar relationship.

In accordance with either of these aspects, the derived signal qualitycan be used to alter one or more receiver characteristics of a receiverused to capture the modulated signal.

Additional aspects and advantages of this invention will be apparentfrom the following detailed description of preferred embodimentsthereof, which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a transceiver 100 including anantenna and a data interface according to an embodiment of theinvention.

FIG. 2 is a more detailed functional block diagram of the symbolprocessor shown in FIG. 1.

FIG. 3 is a flowchart illustrating signal quality determinationaccording to an embodiment of the invention.

FIG. 4 diagrammatically illustrates modified sequential comparisonprocessing used to determine the maximum and next-maximum correlationcandidates according to an embodiment of the invention.

FIG. 5 is a plot of example correlation parameters generated by the CCKcorrelation unit 220 shown in FIG. 2 responsive to an 11 Mbps modulationrate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Turning first to FIG. 1, FIG. 1 is a functional block diagram of an IEEE802.11b compliant transceiver 100 including an antenna 105 and datainterface (e.g. MAC interface 160) according to an embodiment of theinvention. This transceiver can form an operational part of a basestation, network interface, or an information processing system as iswell known in the art. As such, the transceiver includes duplex RF unit110 for receiving and transmitting IEEE 802.11b Physical LayerConvergence Procedure (“PLCP”) sublayer frames modulated onto a selectedcarrier frequency in the Industrial, Scientific and Medical (“ISM”) band−2.4 Ghz as is well-known in the art via antenna 105. Though not shownin the figure, RF Unit 110 of the present embodiment includes selectablediversity tuning circuitry and gain control to assist in tailoring RFunit 110 receiver performance in commonly encountered noisy or multipathenvironments. Also as part of the RF unit 110 are RF and IF frequencyup/down converters used in modulating a baseband signal onto theselected carrier frequency for transmission, as well as receiving andextracting the baseband signal 115 (in analog form) from a tuned channelin the ISM band.

The ADC 120 and pulse-shaping FIR 130 complement the functions of the RFunit 110 in a known manner to convert the inbound and still analogbaseband signal 115 into chipped digital form 125 suitable for codedsymbol recognition, demodulation and processing gain signal qualitydetermination consistent with the present invention as performed by thereceive symbol processor 140.

It should be noted here that the digital baseband signal 125 presentsthe data of interest in the form of one or more coded symbols followingone or more coding protocols, still requires further processing beforee.g. received data can be extracted for use by a Media Access Controller(“MAC”, not shown) and higher layers and applications executing on e.g.a local or remote information processor (not shown). To this end, thereceive symbol processor 140 handles symbol decoding/demodulationfunctions consistent with 802.11b coding protocols, including Barkerspreading and the aforementioned CCK protocols. In turn, consistent withthe IEEE 802.11 and 802.11b standards, the descrambler 150 de-whitensinbound data recovered from the symbol processor 140 for delivery to adata interface such as the layer 2 MAC interface 160, the MAC itself andthe aforementioned higher layers.

The transmit pathway includes the scrambler 155 that whitens outbounddata presented by the MAC interface 160 on behalf of the MAC or higherlayer protocols and applications it supports. The so-whitened outbounddata is then coded, modulated and transmitted in sequence by theremaining components of the transmit pathway by the transmit symbolprocessor 145 (encodes whitened outbound data the using one of theaforementioned symbol modulation techniques depending on the selectedtransmission rate), FIR 135 and DAC 126 (converts the so-coded outbounddata to analog baseband form) and the RF modulator (not shown) andtransmitter (not shown) of the RF unit 110.

The receive pathway, namely the receiver components of RF unit 110 (notshown), the ADC 120, the FIR 130, the receive symbol processor 140, andthe descrambler 150 could be implemented in an alternative embodiment asa discrete receiver coupled to the MAC interface 160. Likewise, theaforementioned components of the transceiver transmit pathway can beimplemented as a discrete transmitter coupled to the MAC interface 160.

Also, in this embodiment, the receive symbol processor 140 isresponsible for determining and maintaining signal quality perceived atthe post-processing or symbol decode/demodulation stage. In particular,the receive symbol processor 140 includes a signal quality derivationunit (FIG. 2) to develop and selectively maintain a measure of thesignal quality representative of the received symbol modulated signal(either baseband and/or carrier modulated). This signal qualityderivation unit 270, to be discussed in more detail with reference toFIG. 2, will provide this signal quality (“SQ2”) to the MAC and higherlayers, applications and/or services (collectively “MAC+ layers”) whichthe transceiver 100 supports via MAC interface 160. In an alternativeembodiment, the receive symbol processor 140 may communicate with theMAC interface 160 “in-band” by including the signal quality informationwithin the data decoded from one or more given symbols it delivers tothe scrambler 150.

In the embodiment shown in FIG. 1, upon instruction by the MAC+layers asconveyed by MAC interface 160, the receive symbol processor 140 may alsodirect the RF unit 110 to alter one or more characteristics of thereceiver environment within the command of the RF unit 110 (such asdiversity tuning and/or gain control) in an effort to redress poorsignal quality as reflected by e.g. SQ2. The receive symbol processor140 does so by issuing an appropriate directive (labeled RF_CNTL)directly to the RF unit 110. In an alternative embodiment, the symbolprocessor may include the directive in-band as part of outbound datathat is coded and delivered to the FIR 130/DAC 120 tandem and then ontothe RF unit 110.

A more detailed discussion of the relevant functions and composition ofthe receive symbol processor 140 according to the embodiment shown inFIG. 1 is now deemed appropriate. Referring now to FIG. 2, FIG. 2illustrates in more detail the symbol decoding/demodulation and signalquality determination features of the receive symbol processor 140according to the present embodiment. As shown in FIG. 2, the receivesymbol processor includes four major components: 1) the decided symboldetermination unit 232 (used to decide a Barker encoded symbol in thedigital chipped baseband signal 125); 2) the candidate determinationunit 225 (determines the maximum correlation and next-maximumcorrelation candidates as well as the decided CCK encoded symbol basedon such candidates found in the signal 125); 3) a scalar calculationunit 286 which uses decided symbol and correlation candidate informationto calculate a scalar relationship; and 4) a signal quality derivationunit 270 to derive a signal quality associated with the signal 125 fromthe scalar relationship(s) calculated by the scalar calculation unit286. More detail on the composition and function of each of thesecomponents will be discussed in greater detail below.

Turning first to the determination units 232 and 235, the digitalchipped baseband signal 125 is serially presented (on a per chip basis)by FIR 130 to the demux 210, where based on the expected modulation type(“mod_type” in FIG. 2) for the current symbol, directs the chippedbaseband signal to either the Barker correlator 230 of the decidedsymbol determination unit 232 or the CCK correlator 220 of the candidatedetermination unit 225. In particular, if the current symbol ispositioned within the PLCP header or preamble, or represents PLCP framepayload (e.g. MAC Payload Data Unit or MPDU) modulated at 802.11 baserates (1 Mbps or 2 Mbps), such symbol is decoded using a Barker modedemodulation pathway (Barker correlator 230 in combination with RAKEfilter 240) with the decided symbol determination unit 232. If, however,the symbol represents high-rate (e.g. 5.5 or 11 Mbps) PLCP payload/MPDUdata, the symbol is instead decoded using a CCK demodulation pathway DFE212, serial-to-parallel latch 214, CCK correlator 220 and comparator 250collectively within the candidate determination unit 225.

Considering first the situation where Barker demodulation is needed, theBarker correlator 230-RAKE filter 240 produces a decided symbol incomplex vector form (Re+jIm), as is well-known in the art. This decidedsymbol is labeled in FIG. 2 as DECIDED_SYMBOL. The RAKE filter 240presents the decided symbol vector to the DQPSK demodulator 260 forconventional phase decoding considerations as well as the scalarcalculation unit 286 and specifically to comparison unit 274 thereof.The fully symbol decoded data is generated by the DQPSK demodulator 260and sent to the descrambler to regenerate user data bits (i.e. the dataof interest).

The comparison unit 274 of the scalar calculation unit 286 assesses theBarker mode decided symbol in this embodiment by comparing themagnitudes of the real and imaginary parts of the decided symbol vectoragainst one of two selectable thresholds, Th1 (for DBPSK 1 Mbpstransmission rate) and Th2 (for DQPSK 2 Mbps transmission rate) In oneimplementation, Th1 is 0.25 and Th2 is 0.375. Thus, if the magnitude ofeither the real or imaginary components of the decided symbol is lessthan Th1 or Th2 respectively, it is determined that the post-processingsignal quality has degraded and so comparison unit 274 yields true and acounter 278 of the signal quality derivation unit 270 (accessed via mux276) is incremented. Also, in this embodiment, the MAC I/F 160 and MAC+layers serviced by the transceiver 110 are notified of the signalquality degradation through issuance of the SQ2 signal by the SQ2control unit 284 of the signal quality derivation unit 270.Alternatively, other techniques for apprising external resources of theperceived degradation in signal quality may be used, such as making thecontents of the counter 278 accessible upon request or sending anappropriate message downstream as part of or in addition to the decodeddata sent to descrambler 150.

Considering now where the current symbol is CCK-encoded (i.e.mod_type=CCK), the CCK demodulation pathway of the candidatedetermination unit 225 is instead selected. Still referring to FIG. 2,the chips of the current symbol are fed serially from the output of thedemux 210 to the decision feedback equalizer 212 for equalizationpurposes and then on to serial to parallel latch 214. Digital feedbackequalization techniques such as disclosed in U.S. patent applicationSer. No. 10/080,826, filed Feb. 21, 2002, entitled DECODING METHOD ANDAPPARATUS, which is incorporated herein fully by reference, may be usedhere.

Once all chips defining the current CCK modulated symbol have beenequalized and accumulated by the latch 214, the latch releases them inparallel to the CCK correlator 220 of the candidate determination unit225. The CCK correlator 220 correlates the chips of the current symbolagainst a plurality of possible candidate vectors, each representing apossible CCK symbol to decide which symbol was received. The pluralityof possible candidate vectors is defined here as a subset of the orderedset of 64 CCK symbol vectors selected based on at least onecharacteristic of the modulated signal bearing the symbol of interest,such as the CCK modulation transmission rate (here either 5.5 Mbps or 11Mbps, labeled as tran_rate(CCK) in FIG. 2). For example, it is knownthat only 4 out of the 64 CCK symbol vectors are possible candidates in5.5 Mbps transmission rate, so only these symbol vectors need becorrelated against the input chips of the symbol. However, in 11 Mbpssituations, all 64 CCK symbol vectors are valid, and thus the possiblecandidate vectors expands to the whole set of CCK symbol vectors.

Consistent with the present embodiment, several techniques may be usedto single out the possible candidate vectors, including parallelcorrelation against the entire set of CCK symbol vectors followed byselective comparison of correlation results involving only the possiblecandidate vectors, flagging the possible candidates presented in alarger table accommodating the entire set of CCK symbol vectors andcorrelating only these candidates against the latched symbol chips, etc.Herein, the set of CCK symbol vectors may be conveniently set forth in alookup table such a vector table (“VT”) 224 within or accessible to theCCK correlator 220, and the subset of possible candidate vectors may beflagged therein by an internal candidate manager agent 222.

Though not required, the CCK correlator 220 and more specifically thevector analysis unit 226 thereof here correlates the chips of the symbolby computing the dot product between these chips and at least thepossible candidate vectors. A resulting correlation parameter isgenerated by this unit 226 for each of the possible candidate vectors,consisting of the sum of the real and imaginary scalar results of thedot product process. As is known in the art, the candidate vector whosecorrelation parameter has the highest value is considered to be the“most correlated vector”, the “best match” or the “maximum correlationcandidate” (as is used herein and labeled “MAX” in FIG. 2). The maximumcorrelation candidate index is then mapped to the data bits d2-d7, andalong with data bits d0-d1 resolved by the DQPSK demodulator 260,completes the data octet corresponding to the current CCK symbol. Thisoctet is sent to the descrambler 150 to complete recovery of the data ina known manner.

More detail on correlation processing may be found in e.g. U.S. patentapplication Ser. No. 10/092,971, filed Mar. 5, 2002, naming Guorong Hu,Yungping Hsu, and Weishi Feng as co-inventors and entitled METHOD ANDAPPARATUS FOR COMPLEMENTARY CODE KEYING, which is incorporated hereinfully by reference.

As discussed above, signal quality consistent with the presentembodiment may be realized through comparative vector analysis of themaximum correlation candidate and the next-maximum correlationcandidate(s), defined herein as one or more possible candidate vectorshaving the relatively next-highest correlation parameter value(labeled“MAX2”). In particular, a scalar relationship between the maximum andnext-maximum correlation candidates is calculated in order to derive themeasure of signal quality.

To better understand the relationship between the maximum correlationcandidate and the next-maximum correlation candidate, consider a sampleplot of correlation parameters produced by a CCK correlator 220 on acomplex plane, wherein angle φ1=1+j, φ2=φ3=φ4=0 at 11 Mbps transmissionrate, as depicted in FIG. 5. The maximum correlation candidate vectorout of 64 possible candidate vectors has a correlation parameter of 16(|8|+|8| point 500), each of 18 next-maximum correlation candidatevectors (not every matching correlation parameter is shown) has acorrelation parameter of 8 (e.g. |8|+|0|—point 505, |4|+|4≢—point 510,|0|+|8|—point 515, |−4|+|4|—point 520, |4|+|−4|—point 525 along outerdiamond 530. In addition, there are 8 possible candidate vectors with acorrelation parameter of 4 (e.g. points 550, 555, 560, 565 along innerdiamond 570), and finally 37 candidates 580 with a correlation parameterof 0. Details of how to find the next-maximum correlation candidate inaccordance with the present embodiment will be discussed below withreference to FIG. 4.

In the embodiment of FIG. 2, the scalar calculation unit 286 and thecomparison unit 280 thereof, in particular, calculates a scalarrelationship for the current CCK encoded symbol signal quality for CCKencoded symbols by comparing the difference between the correlationparameters generated by the vector analysis unit 226 of the CCKcorrelator 220 for the maximum and next-maximum correlation candidateswith a preselected threshold, here Th5.5 as 0.5 (5.5 Mbps transmissionrate) and Th11 (11 Mbps transmission rate) as 0.375. If this difference(a type of scalar relationship) is less than the respective thresholdbased on the present transmission rate, the signal quality is perceivedto have degraded and the comparison unit 280 instructs the counter 278of the signal quality derivation unit 270 to increment (again throughmux 276). Likewise, the SQ2 control unit 284 of the signal qualityderivation unit 270 notifies the MAC interface 160 either directly orindirectly that the signal quality has degraded, and may, upon directionof the MAC or higher layers or applications the transceiver isservicing, may direct the RF unit 110 to alter one or more receivercharacteristics.

It should be noted that the components of the receive symbol processor140, including but not limited to, the aforementioned decided symboldetermination unit 232, the candidate determination unit 225, the scalarcalculation unit 286, and the signal quality derivation unit 270, in theembodiment depicted in FIG. 2 may be implemented as decisional logiccircuitry capable of performing the signal quality determinationfunctions described herein. In fact, any combination of decisionalcircuitry, including combinations involving one or more intelligentcircuits such as a state machine, and/or general-purpose or specificpurpose information processor(s) programmed in accordance with thedisclosed components 232, 225, 286, and 270 or as specified in theflowchart of FIG. 3, may be utilized to carry out signal qualitydetermination according to the present invention as long as chippedsymbol decoding rates compliant with IEEE 802.11 and/or 802.11b can besupported.

Although not shown in the figures, consistent with the presentembodiment the MAC+ layers serviced by the transceiver 100 maycommunicate with the corresponding transmitter (transmitter generatingthe inbound carrier signal) to alter transmit characteristics such aspower level and/or transmission rate in an effort to improve signalquality. It may do so by embedding appropriate messages in the e.g. MPDUor PLCP preamble/header portions that the corresponding transmitter PHYor MAC may decode, as one with ordinary skill in the art willappreciate. Moreover, the SQ2 control unit 284 may inform these higherlayer services and applications that the signal quality has improved, iffor example, it is determined that the calculated scalar relationship ineither mode exceeds the appropriate threshold.

Moreover, although the present embodiment contemplates certain types ofscalar relationships (e.g. Barker mode—magnitude of the real andimaginary components of the decided symbol vector which is essentially ascalar difference between the decided symbol vector and nil, or CCKmode-difference in correlation parameters for the maximum andnext-maximum correlation candidates), other types of scalarrelationships may be used consistent with the present invention in orderto derive an appropriate measure of signal quality based on perceivedprocessing gain reliability and/or errors. For example, in CCK mode, ascalar or Euclidean distance between maximum and next-maximumcorrelation candidate vectors may be calculated and thresholded todetermine if there's a signal quality problem (again a higher numberindicates a more reliable correlation decision has been reached

Turning now to FIG. 3, FIG. 3 is a flowchart describing post symbolprocessing signal quality according to another embodiment of theinvention. In this embodiment, the receive symbol processor 140 mayinclude an ASIC and/or a programmed information processor such as amicroprocessor or microcontroller designed to execute the sequence ofsteps described in the flowchart of FIG. 3, and or any subset thereof incombination with one or more components of the receive symbol processor140 described above.

FIG. 4 illustrates comparison processing carried out by the comparator250 which leverages the relative distance characteristics of CCKreferred to herein as modified sequential comparison processing. First,consider a brute-force or sequential comparison processing in which thecorrelation parameters generated by the CCK correlation 220 are comparedin sequential CCK symbol vector order to find the maximum correlationcandidate from the subset of possible candidate vectors, which in thecase of 11 Mbps transmission rate, requires comparison of 64 correlationparameters. Thus, 63 comparisons must be made to find the maximumcorrelation candidate then, one or more of the next maximum correlationcandidates may be found by disregarding the correlation parameter forthe maximum correlation candidate and again looking for those possiblecandidate vectors which have the largest remaining correlationparameters. Using this technique, another 62 comparisons must be made.

However, by exploiting relative distance relationships within subsets ofCCK vectors, one can group together and re-order comparisons accordingto a second order (depicted as order 401, 411, 421, 431 handled by groupselection logic 408, 418, 428, or 438 respectively). Again assuming thesubset of possible candidate vectors corresponds with the 64 member setof CCK symbol vectors, comparison can be localized to within 4 groups(400, 410, 420 and 430) of 16 sequential vectors (0-15, 16-31, 32-47,and 48-63) differentiated by the value of φ3 using the aforementionedgroup selection logic 408, 418, 428, and 438 respectively, and can befurther localized within each 16 vector group to 4 subgroups of fourvector comparisons. Because of this grouping approach and the reorderedinitial comparisons, each four vector comparison subgroup cannot provideboth the maximum and the next maximum correlation candidate, since eachvector in each subgroup are “uncorrelated” with each other—in otherwords, they are defined by a relative maximum Euclidean distance fromanother. If one of the vectors in one of these subgroups is found to beMAX, it is very unlikely that MAX2 will be in this subgroup. By usingthis approach, the total number of comparisons can be reduced from 125to 73.

Consider first the set of possible candidate vectors defined where φ3=0.In this case, group of vectors 0-15 (group 400) are compared out ofsequence using order 401 provided by group selection logic 408. As shownin FIG. 4, the reordered vector subgroups include 0, 2, 8, 10 (subgroup402), 1, 3, 9, 11 (subgroup 403), 4, 6, 12, 14 (subgroup 404), and 5, 7,13, 15 (subgroup 405). For each subgroup, the correlation parameters ofthe first two and the last two members are compared (e.g. 0-2 and 8-10for subgroup 402, 1-3 and 9-11 for subgroup 403, 4-6 and 12-14 forsubgroup 404 and 5-7 and 13-15 for subgroup 405), and then the larger ofeach pair is then compared to find a subgroup maximum correlationparameter. The local maximum and next maximum correlation parameters(labeled as max_0 and max2_0 in FIG. 4 respectively) for vector group400 are then selected using sequential comparison of the four subgroupmaximum correlation parameters.

The local maximum for the remaining vector groups 410, 420, and 430 canbe then determined in sequence taking into consideration the followingobservations. First, except for the first group 400, the local maximumand next maximum (max_1, max2_1 in group 410; max_2, max2_2 in group420; max_3, max2_3) are selected using sequential comparison taking intoaccount the respective four subgroup maximum correlation parametersalong with the max and max2 correlation parameters from the immediatelypreceding group. For example, in the case of vector group 410, thesubgroup maximum correlation parameters for subgroups 412, 413, 414, and415 are sequentially compared against the max_0 and max2_0 values tofind the max_1 and max2_1 correlation parameters.

According to this embodiment, the modified sequential comparison processcontinues until the maximum max_3 and next maximum max2_3 correlationparameters are obtained with reference to subgroup 430. In this process,the possible candidate vector corresponding to the max_3 correlationparameter is deemed the maximum correlation candidate and the possiblecandidate vector(s) corresponding to the max2_3 correlation parameterare deemed the next maximum correlation candidate.

It will be obvious to those having ordinary skill in the art that manychanges may be made to the details of the above-described embodiments ofthis invention without departing from the underlying principles thereof.For example, though the above-described embodiments are directed toimplementations compliant with IEEE 802.11 and 802.11b standard, theteachings of the present invention are not intended to be so limitingand in fact post symbol processing signal quality consistent with thepresent invention can be derived in other coded symbol receptionscenarios and environments, whether based on RF transmission orotherwise. The scope of the present invention should, therefore, bedetermined only by the following claims.

1. A method for operating a symbol processor, the method comprising:determining maximum and next-maximum correlation candidates for a symbolof a modulated signal; calculating a scalar relationship between themaximum and next-maximum correlation candidates; deriving signal qualityassociated with the modulated signal based on the scalar relationship;and altering a characteristic based on the derived signal quality usinga circuit of the symbol processor.
 2. The method of claim 1 wherein thecharacteristic comprises a transmitter characteristic.
 3. The method ofclaim 2 wherein the transmitter characteristic comprises at least one ofpower level and transmission rate.
 4. The method of claim 1 furthercomprising: embedding data in a frame wirelessly transmitted by areceiver to a transmitter, wherein altering a characteristic comprisesaltering a transmitter characteristic based on the data.
 5. The methodof claim 1 wherein the symbol is defined by a plurality of chips; andwherein the determining step comprises: correlating the plurality ofchips of the symbol with a plurality of possible candidate vectors;selecting as a maximum correlation candidate one of the plurality ofpossible candidate vectors most correlated to the plurality of chips ofthe symbol; and selecting as a next-maximum correlation candidate atleast one of the plurality of possible candidate vectors other than themaximum correlation candidate.
 6. The method of claim 5 furthercomprising deriving the plurality of possible candidate vectors from aset of symbol vectors based on at least one characteristic of themodulated signal.
 7. The method of claim 6 wherein the correlatingincludes generating a correlation parameter for each of the plurality ofpossible candidate vectors with respect to the plurality of chips of thesymbol, wherein the selecting comprises assessing the correlationparameters using one of: a sequential comparison process following afirst order of the set of symbol vectors; and a modified sequentialcomparison process following a second order of the set of symbolvectors, wherein the second order is different than the first order. 8.The method of claim 7 wherein the second order is defined with respectto at least one subset of the set of symbol vectors, and wherein the atleast one subset includes plural members of the set of symbol vectorsselected in accordance with a relative distance relationshiptherebetween.
 9. The method of claim 1 wherein the symbol comprises acomplementary code keyed symbol compliant with IEEE 802.11b (1999). 10.The method of claim 1 wherein the scalar relationship comprises at leastone of: a distance between the maximum and next-maximum correlationcandidates; and a magnitude difference between the maximum andnext-maximum correlation candidates.
 11. The method of claim 4 furthercomprising: receiving the modulated signal in accordance with a receivercharacteristic; and modifying the receiver characteristic based on thederived signal quality.
 12. A method for operating a symbol processor,the method comprising: determining a decided symbol for a symbolperceived within a modulated signal; calculating a scalar relationshipbetween a vector corresponding to the decided symbol and a reference;deriving signal quality associated with the modulated signal based onthe scalar relationship; and altering a characteristic based on thederived signal quality using a circuit of the symbol processor.
 13. Themethod of claim 12 wherein the characteristic comprises a transmittercharacteristic.
 14. The method of claim 13 wherein the transmittercharacteristic comprises at least one of power level and transmissionrate.
 15. The method of claim 12 further comprising: embedding data in aframe wirelessly transmitted by a receiver to a transmitter, whereinaltering a characteristic comprises altering a transmittercharacteristic based on the data.
 16. The method of claim 12 wherein thederiving step comprises: comparing the scalar relationship to athreshold; generating a first signal if the scalar relationship is lessthan the threshold; and generating a second signal if the scalarrelationship is greater than or equal to the threshold.
 17. The methodof claim 16 further comprising: receiving the modulated signal inaccordance with a receiver characteristic; and modifying the receivercharacteristic when the derived signal quality comprises the firstsignal.
 18. The method of claim 15 further comprising: receiving themodulated signal in accordance with a receiver characteristic; andmodifying the receiver characteristic based on the derived signalquality.
 19. The method of claim 12 wherein the symbol comprises acomplementary code keyed symbol compliant with IEEE 802.11b (1999). 20.A symbol processor comprising: a candidate determination unit todetermine maximum and next-maximum correlation candidates for a symbolof a modulated signal; a scalar calculation unit to calculate a scalarrelationship between the maximum and next-maximum correlationcandidates; a signal quality derivation unit to derive a signal qualityassociated with the modulated signal based on the scalar relationship;and a circuit to alter a characteristic based on the derived signalquality.
 21. The symbol processor of claim 20 wherein the characteristiccomprises a transmitter characteristic.
 22. The symbol processor ofclaim 21 wherein the transmitter characteristic comprises at least oneof power level and transmission rate.
 23. The symbol processor of claim20 wherein the circuit embeds data in a frame wirelessly transmitted toa transmitter to alter a transmitter characteristic of the transmitterbased on the data.
 24. The symbol processor of claim 20 wherein: thesymbol is defined by a plurality of chips; and the candidatedetermination unit comprises: a correlator to correlate the plurality ofchips of the symbol with a plurality of possible candidate vectors; anda comparator that selects as a maximum correlation candidate one of theplurality of possible candidate vectors most correlated to the pluralityof chips of the symbol and that selects as the next-maximum correlationcandidate at least one of the plurality of possible candidate vectorsother than the maximum correlation candidate.
 25. The symbol processorof claim 24 wherein the correlator further comprises a candidate managerto derive the plurality of possible candidate vectors from an orderedset of symbol vectors based on at least one characteristic of themodulated signal.
 26. The symbol processor of claim 25 wherein; thecorrelator includes a vector analysis unit to generate a correlationparameter for each of the plurality of possible candidate vectors withrespect to the plurality of chips of the symbol, wherein the comparatorcomprises assesses the correlation parameters using one of: a sequentialcomparison process following a first order of the set of symbol vectors;and a modified sequential comparison process following a second order ofthe set of symbol vectors, wherein the second order is different thanthe first order.
 27. The symbol processor of claim 26 wherein the secondorder is defined with respect to at least one subset of the set ofsymbol vectors, and wherein the at least one subset includes pluralmembers of the set of symbol vectors selected in accordance with arelative distance relationship therebetween.
 28. The symbol processor ofclaim 20 wherein the symbol comprises a complementary code keyed symbolcompliant with IEEE 802.11b (1999).
 29. The symbol processor of claim 20wherein the scalar relationship comprises at least one of: a distancebetween the maximum and next-maximum correlation candidates; and amagnitude difference between the maximum and next-maximum correlationcandidates.
 30. The symbol processor of claim 20 further comprising: adecided symbol determination unit to determine a decided symbol for thesymbol perceived within the modulated signal, wherein the scalarcalculation unit calculates a second scalar relationship between avector corresponding to the decided symbol and a reference, wherein thesignal quality derivation unit derives a second signal qualityassociated with the modulated signal based on the second scalarrelationship.
 31. The symbol processor of claim 30 wherein the scalarcalculation unit comprises a comparison unit coupled to the decidedsymbol determination unit to compare the scalar relationship to athreshold and to generate one of a first signal if the second scalarrelationship is less than the threshold and a second signal if thesecond scalar relationship is greater than or equal the threshold.
 32. Asymbol processor comprising: a candidate determination unit to determinemaximum and next-maximum correlation candidates for a symbol of amodulated signal; a scalar calculation unit to calculate a scalarrelationship between the maximum and next-maximum correlationcandidates; and a signal quality derivation unit to derive a signalquality associated with the modulated signal based on the scalarrelationship; and a circuit to alter a characteristic based on thederived signal quality.
 33. The symbol processor of claim 32 wherein thecharacteristic comprises a transmitter characteristic.
 34. The symbolprocessor of claim 33 wherein the transmitter characteristic comprisesat least one of power level and transmission rate.
 35. The symbolprocessor of claim 32 wherein the circuit embeds data in a framewirelessly transmitted to a transmitter to alter a transmittercharacteristic of the transmitter based on the data.
 36. The symbolprocessor of claim 32 wherein the characteristic comprises a receivercharacteristic.
 37. The symbol processor of claim 32 wherein the symbolis defined by a plurality of chips; and wherein the candidatedetermination unit comprises: a correlator to correlate the plurality ofchips of the symbol with a plurality of possible candidate vectors; anda comparator that selects as a maximum correlation candidate one of theplurality of possible candidate vectors most correlated to the pluralityof chips of the symbol and that selects as a next-maximum correlationcandidate at least one of the plurality of possible candidate vectorsother than the maximum correlation candidate.
 38. The symbol processorof claim 37 wherein the correlator further comprises a candidate managerto derive the plurality of possible candidate vectors from an orderedset of symbol vectors based on at least one characteristic of themodulated signal.
 39. The symbol processor of claim 38 wherein: thecorrelator includes a vector analysis unit to generate a correlationparameter for each of the plurality of possible candidate vectors withrespect to the plurality of chips of the symbol; and wherein thecomparator assesses the correlation parameters using one of: asequential comparison process following a first order of the set ofsymbol vectors; and a modified sequential comparison process following asecond order of the set of symbol vectors, wherein the first and secondorders are different.
 40. The symbol processor of claim 39 wherein thesecond order is defined with respect to at least one subset of the setof symbol vectors, and wherein the at least one subset includes pluralmembers of the set of symbol vectors selected in accordance with arelative distance relationship therebetween.
 41. The symbol processor ofclaim 32 wherein the symbol comprises a complementary code keyed symbolcompliant with IEEE 802.11b (1999).
 42. The symbol processor of claim 32wherein the scalar relationship comprises at least one of: a distancebetween the maximum and next-maximum correlation candidates; and amagnitude difference between the maximum and next-maximum correlationcandidates.
 43. The symbol processor of claim 32 wherein the symbolprocessor further comprises: a decided symbol determination unit todetermine a decided symbol for the symbol perceived within the modulatedsignal, wherein the scalar calculation unit calculates a second scalarrelationship between a vector corresponding to the decided symbol and areference, and wherein the signal quality derivation unit derives asecond signal quality associated with the modulated signal based on thesecond scalar relationship.
 44. The symbol processor of claim 43 whereinthe scalar calculation unit comprises a comparison unit coupled to thedecided symbol determination unit to compare the scalar relationship toa threshold and to generate one of a first signal if the second scalarrelationship is less than the threshold and a second signal if thesecond scalar relationship at least meets the threshold.